Since emergence of the first laser, profound reformation has taken place in human communication. As a carrier of information, light enables human communication to be timely and convenient because the light features a high speed and stability. With development of science and technology, disadvantages in aspects of power consumption and a duty cycle gradually appear in conventional module optics. Integration in multiple materials has been tried in optical path design, but is limited in development because of a technology limitation. However, silicon optics draws concern because of its compatibility with a circuit technology. People expect that integrated optics can have a same path as electricity in terms of silicon.
The silicon light can be applied to large-scale and high-density integration due to a high refractive index contrast ratio. In addition, the silicon light can further use a mature complementary metal oxide semiconductor (CMOS) technology of an electric chip, so that the silicon light has a unique advantage. However, an optical path does not have flexibility of the circuit. In a large-scale switch matrix, cross of waveguides cannot be avoided. On a silicon light platform, a cross waveguide is an extremely core device. If a loss value of one cross waveguide is 0.3 dB, and if a quantity of cross waveguides in a switch matrix is 100, a loss caused merely by the cross waveguides is 30 dB, which is a great loss. Therefore, it is extremely necessary to reduce a cross waveguide loss.
In the prior art, an objective of reducing the cross waveguide loss is achieved by using a cross waveguide based on mode broadening. Broadening of an optical wave mode is implemented by using a change of a waveguide structure, that is, a width of a core layer broadens towards a cross area and a shallow etching part increases, so that a change of optical wave field distribution is achieved to reduce optical divergence in the cross area. A cross waveguide based on multimode interference is further used in the prior art, that is, the cross waveguide is a multimode waveguide in the cross area, and is a single-mode waveguide at an input end and an output end, so that the objective of reducing the cross waveguide loss is achieved. That is, waveguides at the input end and the output end of the cross waveguide are single-mode waveguides, and a waveguide in the cross area is a multimode waveguide. Image points generated by means of the multimode interference are used to reduce an optical wave loss in the cross area. However, in the prior art, an extra loss is brought because of a change of field distribution and a change of a waveguide mode.